When each picture contained in video data has color components, a color space called YUV, for example, is used to represent the luminance and chromaticity of each pixel of the picture. In YUV, each pixel in a picture is represented by the values of the luminance component Y and two color difference components U and V. YUV image formats include a format known as YUV 444 in which no pixels are decimated to represent the color difference components, and other formats such as YUV 420 and YUV 422 in which pixels are decimated to represent the color difference components.
Video data represented in YUV 420 format is irreversible (lossy) video data whose chrominance information is degraded from that of the original video data. On the other hand, video data represented in YUV 444 format is lossless video data whose chrominance information is not degraded from that of the original video data. However, in the case of video data represented in YUV 444 format, the amount of data used to represent the color difference components U and V is four times as large as the amount of data that would be used to represent the color difference components U and V if the same video data were to be represented in YUV 420 format.
It is therefore preferable to use video data represented in YUV 444 format if the video data is to be encoded so as to minimize the difference between the chrominance information of the original video data and the chrominance information of the video data obtained by decoding the once encoded video data. However, a decoding computer program or decoding apparatus used to decode the encoded video data may be compatible with YUV 420 format but may not be compatible with YUV 444 format. In view of this, it is preferable to encode video data so that the video data can be reproduced in both YUV 444 and YUV 420 formats. On the other hand, in the prior art, there is proposed a technique that generates an image having a higher resolution than an image obtained in advance (for example, refer to Japanese Laid-open Patent Publication No. 2011-118908).